Ventilation systems: design and peformance

Ventilation Systems

Design and performance

Edited by Hazim B. Awbi

Ventilation Systems

Properly designed ventilation systems for cooling, heating and cleaning

the outdoor air supplied to buildings are essential for maintaining good

indoor air quality as well as for reducing a building’s energy consumption.

Modern developments in ventilation science need to be well understood

and effectively applied to ensure that buildings are ventilated as efficiently

as possible.

Ventilation Systems provides up-to-date knowledge based on the

experience of internationally recognised experts to deal with current and

future ventilation requirements in buildings. Presenting the most recent

developments in ventilation research and its applications, this book offers a

comprehensive reference to the subject, covering the fundamentals as well

as more advanced topics. It is a unique publication as it covers the subject

rigorously in a way needed by researchers but has a practical flavour that

will be of value to a wide range of building professionals.

Hazim B. Awbi is Professor of Building Environmental Science at the

University of Reading, UK, and founder of the Indoor Environment and

Energy Research Group (IEERG).

Also available from Taylor & Francis

Ventilation of Buildings 2nd edition

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Tropical Urban Heat Islands

N. H. Wong et al. Hb: ISBN 978–0–415–41104–2

Heat and Mass Transfer in Buildings

K. Moss Hb: ISBN 978–0–415–40907–0

Pb: ISBN 978–0–415–40908–7

Energy Management and Operating Costs in Buildings

K. Moss Hb: ISBN 978–0–415–35391–5

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J. Twidell and T. Weir Hb: ISBN 978–0–419–25320–4

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Mechanics of Fluids 8th edition

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Ventilation Systems

Design and performance

Edited by Hazim B. Awbi

First published 2008

by Taylor & Francis

2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN

Simultaneously published in the USA and Canada

by Taylor & Francis

270 Madison Ave, New York, NY 10016, USA

Taylor & Francis is an imprint of the Taylor & Francis Group, an informa

business

© 2008 Taylor and Francis, editorial material; individual chapters, the

contributors

All rights reserved. No part of this book may be reprinted or

reproduced or utilised in any form or by any electronic, mechanical, or

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The publisher makes no representation, express or implied, with regard

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omissions that may be made.

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data

Ventilation systems: design and performance / edited by Hazim B. Awbi.

p. cm.

Includes bibliographical references and index.

ISBN-13: 978-0-419-21700-8 (hardback : alk. paper) 1. Ventilation.

I. Awbi, H. B. (Hazim B.), 1945–

TH7658.V455 2007

697.9

2–dc22

2006100008

ISBN10: 0–419–21700–2 (hbk)

ISBN10: 0–203–93689–2 (ebk)

ISBN13: 978–0–419–21700–8 (hbk)

ISBN13: 978–0–203–93689–4 (ebk)

This edition published in the Taylor & Francis e-Library, 2007.

“To purchase your own copy of this or any of Taylor & Francis or Routledge’s

collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.”

ISBN 0-203-93689-2 Master e-book ISBN

Contents

List of contributors viii

Preface ix

Acknowledgements xi

1 Airflow, heat and mass transfer in enclosures 1

YUGUO LI

1.1 Introduction 1

1.2 Transport phenomena in buildings 2

1.3 General governing equations of airflow,

heat and mass transfer 8

1.4 Turbulence and its modeling 26

1.5 Jets, plumes and gravity currents 41

1.6 Solution multiplicity of building airflows 45

1.7 Experimental methods 51

References 56

Nomenclature 58

2 Ventilation and indoor environmental quality 62

BJARNE OLESEN, PHILO BLUYSSEN AND CLAUDE-ALAIN ROULET

2.1 Introduction 62

2.2 Indoor environmental quality 63

2.3 Indoor air quality 64

2.4 Thermal comfort 78

2.5 Indoor environment and performance 95

References 99

3 Energy implications of indoor environment control 105

CLAUDE-ALAIN ROULET

3.1 Introduction 105

3.2 Energy flow in buildings 106

vi Contents

3.3 Assessing energy flows 116

3.4 Energy and indoor environment quality 121

3.5 Strategies for HVAC systems and components 137

3.6 Heat recovery 140

3.7 Effect of ventilation strategies on the energy use 146

3.8 Summary 150

Notes 151

References 151

Nomenclature 153

4 Modeling of ventilation airflow 155

JAMES AXLEY AND PETER V. NIELSEN

4.1 Introduction 155

4.2 Microscopic methods 156

4.3 Macroscopic methods 189

References 249

Nomenclature for macroscopic methods 260

5 Air distribution: system design 264

PETER V. NIELSEN AND HAZIM B. AWBI

5.1 Introduction 264

5.2 The room and the occupied zone 265

5.3 The qo–
To relationship for the design

of air distribution systems in rooms 267

5.4 Design of mixing ventilation 268

5.5 Design of displacement ventilation 276

5.6 Design of high momentum displacement ventilation 284

5.7 Design of vertical ventilation 288

5.8 Comparison between different air distribution systems 292

References 297

6 Characteristics of mechanical ventilation systems 300

CLAUDE-ALAIN ROULET

6.1 Introduction 300

6.2 Types of ventilation systems 300

6.3 Temperature and humidity control with

mechanical ventilation (air-conditioning) 303

6.4 Components of air-handling units 306

Contents vii

6.5 Airflow rate measurements in ventilation systems 324

6.6 Summary 342

References 343

Nomenclature 344

7 Characteristics of natural and hybrid ventilation systems 345

PER HEISELBERG

7.1 Introduction 345

7.2 Ventilation concepts 349

7.3 System solutions and characteristics 352

7.4 Ventilation components 365

7.5 Control strategies 374

7.6 Examples 379

References 398

8 Measurement and visualization of air movements 400

CLAUDE-ALAIN ROULET

8.1 Introduction 400

8.2 Air velocity measurement 400

8.3 Measuring air tightness 407

8.4 Visualization of air movement 415

8.5 Age of air and air change efficiency 418

8.6 Mapping the age of air in rooms 428

8.7 Summary 435

References 436

Nomenclature 437

Index 439

Contributors

Hazim B. Awbi, Ph.D. is Professor of Building Environmental Science in

the School of Construction Management and Engineering, University

of Reading, UK, and founder of the Indoor Environment and Energy

Research Group (IEERG). His research is in ventilation, room air

movement, Computational Fluid Dynamics (CFD) and heat transfer

in buildings.

James Axley, Ph.D. is Professor at the School of Architecture and the School

of Forestry and Environmental Studies, Yale University, USA and his

research is on the development of theory and computational tools for

building thermal, airflow, and air quality simulation and design analysis.

Philomena Bluyssen, Ph.D. is a Research Scientist at TNO, Netherlands

and has published extensively on indoor air quality.

Per Heiselberg, Ph.D. is Professor in the Department of Civil Engineering

andHead ofHybrid Ventilation Centre at Aalborg University, Denmark.

Yuguo Li, Ph.D. is Professor in the Department of Mechanical Engineer￾ing, University of Hong Kong and his research is in natural ventilation,

CFD, bio-aerosols and engineering control of respiratory infection.

Peter V. Nielsen, Ph.D., FASHRAE is Professor at Aalborg University,

Denmark and Honorary Professor at the University of Hong Kong. His

research is in room air movement and Computational Fluid Dynamics

(CFD). He was awarded the John Rydberg Gold Medal in 2004.

Bjarne W. Olesen is Professor and Head of the International Centre for

Indoor Environment and Energy, Department of Mechanical Engineer￾ing, Technical University of Denmark. The Centre is one of the world’s

leading research centres in indoor environment, people’s health, com￾fort and productivity.

Claude-Alain Roulet, Ph.D., is Adjunct Professor at the EPFL (Swiss

Federal Institute of Technology, Lausanne), Switzerland and private

consultant in building physics and indoor environment quality.

Preface

This book is authored by eight distinguished researchers in ventilation and

indoor air quality from five countries. It is a follow-on from the success￾ful book Ventilation of Buildings, which is authored by the title editor.

The new title draws from the vast experience of the eight authors in the

field, includes their knowledge of the subject and presents the results from

extensive international research programmes involving the authors as well

as results from the work of other researchers.

The book deals with the applications of ventilation science in buildings.

Buildings are responsible for a large proportion of a country’s total energy

consumption and a large part of this is used in ventilation, i.e. heating,

cooling and cleaning of outdoor air supplied to buildings. Properly designed

ventilation systems are essential for maintaining good indoor air quality,

which is necessary for a productive building as well as for reducing a build￾ing’s energy consumption. To achieve these aims, it is essential that modern

development in ventilation science is well understood and effectively applied

by those involved in building and system design and maintenance. This

book aims to provide the building professionals with up-to-date knowledge

based on the experience of internationally recognised experts to enable them

implementing current and future ventilation requirements in buildings.

The book covers the fundamentals as well as the more advanced topics

to cater for a wide range of readers. This unique publication covers the

subject rigorously in a way needed by researchers and, at the same time, has

a practical flavour and therefore should appeal to a wide range of building

professionals. The book offers a comprehensive reference for researchers,

designers, architects and specifiers of ventilation systems in buildings.

Chapter 1 presents the fundamental principles and physics of the air￾flow and heat transfer phenomena that occur within buildings. The basic

fluid flow and heat transfer concepts and their analyses are presented with

worked examples giving particular emphasis to the flow in enclosures.

Chapter 2 presents the latest knowledge on human requirements for ther￾mal comfort and air quality indoors and the impact of these on ventilation

rates. The results and arguments presented in Chapter 2 show that there is

x Preface

a tendency for specifying higher fresh air supply rates in buildings than is

recommended by most current ventilation guidelines. This will undoubtedly

have a large impact on energy usage, which will require a proper assessment

of the energy flow for ventilation to mitigate the impact. Chapter 3 describes

methods used for assessing the energy flow in buildings and ventilation

systems. It presents guidelines for improving the energy performance of

buildings without compromising the indoor environment. Chapter 4 intro￾duces the modeling of airflow into and within buildings by describing two

categories of models that are commonly used nowadays: the macroscopic

and the microscopic approaches. Whereas the macroscopic methods are

based on modeling the air flow in buildings including their heating, ven￾tilating and air-conditioning (HVAC) systems as collection of finite-sized

control volumes, the microscopic methods, which are better known as com￾putational fluid dynamics (CFD) models, on the other hand are based on the

continuum approach that provides detailed descriptions of the flow, heat

and mass transport processes within and outside the building. Chapter 5

deals with the characteristics of different types of air distribution systems,

including new methods that have recently been developed, and the methods

used for selecting and designing these for mechanically ventilated building

enclosures. In Chapter 6, the types of HVAC systems are characterised,

and the methods used for assessing the components of such systems are

described, including the measurement techniques that are used to assess their

performance. Chapter 7 describes the characteristics and performance of

natural and hybrid ventilation systems and their components. Such systems

are finding wider applications in modern buildings as, if properly designed,

these can provide good indoor environment at lower energy consumption

than conventional mechanical systems. Examples of buildings using hybrid

systems are also presented. Finally, Chapter 8 describes various techniques

that are applied in ventilation and room air movement measurements and

airflow visualization. Such techniques are very useful for setting-up, com￾missioning and maintaining ventilation systems as well as estimating the

airflow through the building envelop.

Hazim B. Awbi

Reading, UK, 2007

Acknowledgements

The following figures and tables are reproduced with permission:

Table 2.3 ‘Smoking free spaces in commercial buildings’ according to

ASHRAE 62.1, CR 1752, and EN15251. © American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc., www.ashrae.org

Figure 2.5 (a) de Dear, R. and Brager, G. S. (1998) ‘Developing an adap￾tive model of thermal comfort and preference’, ASHRAE Transactions,

104(1a): 145–167. © American Society of Heating, Refrigerating and Air￾Conditioning Engineers, Inc., www.ashrae.org

Figure 5.25 Nielsen, P. V., Topp, C., Snnichsen, M. Andersen, H. (2005).

‘Air distribution in rooms generated by a textile terminal – comparison with

mixing ventilation and displacement ventilation’. ASHRAE Transactions

111 (Part 1): 733–739. © American Society of Heating, Refrigerating and

Air-Conditioning Engineers, Inc., www.ashrae.org

Chapter 1

Airflow, heat and mass transfer

in enclosures

Yuguo Li

1.1 Introduction

Airflow and transport phenomena play an important role in air quality,

thermal comfort and energy consumption in buildings. Advances in air￾flow control in buildings in the past four decades have made it possible to

design and evaluate building ventilation not only qualitatively but in many

situations also quantitatively. In recent years, a broad range of practical

ventilation problems have been investigated by the application of computa￾tional fluid dynamics (CFD) and advanced airflow measurement methods.

This chapter describes the fundamental principles of airflow, heat and

mass transfer phenomena that take place in buildings. The need of empha￾sizing multi-disciplinary nature is noted here. Much of the basic theory

and concepts on airflow, heat and mass transfer are described in clas￾sical textbooks of heat transfer and fluid mechanics, with new develop￾ments reported in journals such as Journal of Heat Transfer, Journal of

Fluid Mechanics and International Journal of Heat and Mass Transfer.

Historically, the concepts and technologies developed in other engineering

disciplines have also been successfully applied and extended to ventila￾tion application. Examples include the application of the residence time

concept (Danckwerts, 1952) developed in chemical engineering to venti￾lation efficiency (Sandberg, 1981) and the application of CFD originally

developed for the aerospace industry (Nielsen, 1974). Contribution of

the ventilation community to fluid mechanics and heat and mass trans￾fer has also been evident, such as the development of non-isothermal jets

(Koestel, 1955).

The ultimate goal of an in-depth understanding of fluid mechanics in

building airflow is to provide engineers effective and efficient design and

analysis tools. Either experiments or numerical predictions (which may

be considered as numerical experiments) can only provide data, but no

conclusions. It is important that the fundamental principles can be applied

in analysing the data from either experiments or CFD and also drawing

conclusions from data. The quality of data is crucial for drawing any good or

new conclusions. Effective and accurate methods for obtaining the required